The present invention relates to an optical waveguide device suitable for scanning near-field optical microscopes and optical data recorders.
In recent years, a technology using near-field light (light that reaches regions of distances shorter than wavelengths of light) attracts a great deal of attention as a technology for enabling optical treatment of light in a regions smaller than the wavelength of light (visible light: 0.4 to 0.8 micrometers). For example, in the field of scanning near-field optical microscopes, an optical probe made of an optical fiber with a minute opening is used as an optical waveguide device. The size of the opening is less than wavelength of light. When observing a minute area on a surface of a sample, the minute opening of the optical probe is located close to the area so that the field of light (near field) emerging out of the opening contacts the surface of the sample. Then, the minute area of the sample, which is coupled to the near field, is irradiated with the near-field light. Reflected light, scattering light, and transmitted light from the sample are detected so that the area is locally observed and evaluated. Conventionally, various types of optical probes are used for decreased size of data pits of optical recording media such as CDs and for evaluating semiconductor manufacturing processes in which submicron machining is performed.
The size of the distal opening of an optical probe is less than the wavelength of light. Thus, for example in an illumination mode, the intensity of near-field light emerging out of the minute opening is as feeble as one thousandth of light introduced in the optical probe. Light of such optical probe is insufficient for high-speed writing or high-speed reading of optical data recording devices. It is therefore necessary to increase the intensity of near-field light emerging out of the minute opening of the optical probe. However, if a light source with a high intensity is used for increasing the intensity of near-field light, the costs are increased. On the other hand, if the size of the distal opening is increased, the light is spread in a wider area and the resolution is degraded. Neither case therefore cannot eliminates drawbacks in practical use.